1. Field of the Invention
The present invention relates generally to improved sheet feeding and, more specifically, to eliminating image smear, regardless of paper basis weight, in the transfer zone between a prefuser transport and a fuser nip.
2. Description of the Prior Art
In a paper path of a xerographic printing system, positions and profiles of baffles are designed to guide the movement of substrates into functional areas of various subsystems. A typical paper path includes passages from a feeder, through registration, image transfer, prefuser transport, by a fuser entrance baffle into a fuser, then exiting to an output tray. Robust paper handling in the paper path must be performed in a manner which ensures motion quality without image smear and paper jams. However, it is a substantial design challenge for a paper path capable of handling a wide range of substrate sizes and basis weights to meet stringent image quality requirements. It may be preferable to use a sensor system for enabling the adjustments of the paper path parameters according to detected substrate characteristics but such an intelligent system is very costly by reason of the added necessary sensors and other required electrical/mechanical components.
A disclosure relating generally to the field of concern of the instant invention is found in commonly assigned U.S. Patent Application Publication No. US 2002/0076228 to Less et al. although the problem solved by that invention is different from the problem which is of concern to the present invention.
In order to meet copy quality goals for a range of paper weights, paper path control is essential. To avoid adverse effects of paper wrinkle and image deletions, the paper needs to be bent around the prefuser paper guide exit. To avoid image smear with lightweight paper tangency control to the fuser nip is required. Unfortunately this treacherous paper path requirement will result, especially, in heavyweight paper handling problems. There is a different set of geometric paper path control requirements for heavyweight paper than for lightweight paper.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived.
A guide system for xerographic printing apparatus introduces paper bearing an unfixed image and having a broad range of weights into a fuser nip from a prefuser transport without causing image smear. In one embodiment, a baffle member is positioned in the path of the paper advancing toward the fuser nip for engagement by the paper""s leading edge. The baffle member is hinged at its mounting end for swinging movement between a maximal and minimal positions as defined by stop members and is biased into engagement with the minimal stop member. The magnitude of the bias is chosen such that as the lightest weight paper engages the baffle member, it bends around its free end and is guided into the fuser nip, and such that as heavy paper engages the baffle member, it forces the baffle member toward engagement with the second stop member and itself is guided into the fuser nip.
The proposed design concept is to have paper stiffness determine the geometric position of the prefuser paper guide to minimize heavyweight paper lead edge paper impact when contacting the prefuser guide. Maximal and minimal stops are used to control the full range of paper guide movement.
In one instance, as noted, a prefuser paper guide is spring loaded and self adjusting with positioning stops to control the paper path in the region of concern and thereby enables handling a wide range of paper basic weights and sizes without paper handling failures including jams, paper stall, smear and the like while still meeting required critical parameters for paper fusing, that is, avoiding wrinkles, image deletions, smear, and the like.
In short, then, in this particular embodiment, a self-adjusting spring loaded prefuser paper guide is provided to reduce image disturbances that occur when stiff papers are used. The image disturbances are introduced when a stiff sheet contacts the baffle that directs paper from the prefuser transport into the fuser nip, propagating part of the impact force back into the xerographic transfer area. The proposed guide features spring loaded fingers that deflect more for stiff papers than for thin papers, modifying the paper path and absorbing some of the impact force. The benefit which is achieved enables a wide latitude of paper stiffness.
In another instance, a mechanism for eliminating image smear of heavy weight sheets in the transfer zone is achieved by installing self-adjusting guide fingers on the upstream portion of the fuser entrance baffle for softening the impact force of the heavy weight sheets when hitting the baffle such that the images in the transfer zone not be disturbed. More specifically, self-adjusting fingers are incorporated into the prefuser entrance baffle for increasing the paper handling latitude for a large range of light weight and heavy weight papers, such as from 45 to 285 gsm paper basis weight. A plurality of spring-loaded fingers are positioned near the paper landing position in the upstream portion of the fuser entrance baffle. There are slot openings in the corresponding locations of the baffle for accommodating the angular movement of the fingers crossing the baffle. The stiffness of torsion springs is chosen with little deflection of the fingers by the light weight sheets while accommodating significant deflections upon contact by heavy basis weight sheets. The deflection of the fingers softens the contact force, and therefore, with less adverse effect on image quality at the transfer zone. With respect to a given optimized baffle geometry guiding sheets into the fuser nip, the position and the deflection of the fingers can be designed so as not to adversely affect the entry of the sheets into the fuser nip.
In short, then, this alternate embodiment also corrects image disturbances which are introduced when stiff papers contact the baffle that, directs paper from the prefuser transport into the fuser nip, propagating part of the impact force back into the xerographic transfer area. This proposed guide features spring loaded fingers that deflect more for stiff papers than for thin papers, modifying the paper path and absorbing some of the impact force. The resulting benefit of this construction is that printing can occur with excellent image quality on sheet paper having a broad latitude of stiffness.
A primary feature, then, of the present invention is the provision of xerographic printing apparatus provided with improved sheet movement in transfer, prefuser transport, fuser paper path.
Another feature of the present invention is the provision of such a system which operates to eliminate image smear, regardless of paper basis weight, in the transfer zone, between a prefuser transport and a fuser nip.
Yet another feature of the present invention is the provision of such a system for introducing paper having an unfixed image thereon and having a predetermined range of basis weights between a lightest basis weight and a heaviest basis weight into a fuser nip from a prefuser transport and without causing image smear on the paper.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.